Recycling is one of the most environmentally sensible solutions to waste disposal and resource conservation. Many different types of materials can be recycled for reuse, including metals, plastics and paper.
In paper recycling, white copy paper is the most valuable of all recyclable paper grades, while newsprint and file folder stock, which have a high concentration of groundwood, are inferior grades and are considered to be contaminants when found in white copy paper. Thus, during the recycling of high grade white paper, it is desirable that the feed be devoid of high groundwood-content material, which would degrade the finished product. Typically paper sorting is undertaken by workers, who visually identify inferior grades and contaminated white copy paper on a conveyor carrying mixed stock and manually separate inferior grades from the white copy paper.
The separated product inevitably contains an undesirably high content of the inferior grades because visual discrimination is often not very effective, particularly when the conveyor is moving at a high speed. Manual sorting is also undesirable for security reasons, where for example the paper to be recycled contains confidential documents destined for shredding.
Sorting can be done automatically by color detection. However, it is common to encounter groundwood contaminants in the white paper copy paper grade when sorting is based on color, because sensitivity limitations and obscuring of the stock by graphics can result in newsprint and white-colored file folders being graded as white paper.